Imperial vs metric ...
 

I'm trying some cut with my just finished MM, one of my first cut will be some plywood for my "future" boat ... the "Tini Cat" or Philip Bolger's Catboat.
This is the problem: all the mesures are in this form: 1,2,4 I understend that 1=1 feet, 2=2 inch but the third number ? it coud be 4/16 4/32 4/8 I can't understand,. Can somebody who is familiar with Imperil system explain ? on the book I have there is no reference at all (Build the instant catboat by Harold dynamite Payson"
thanks

this is what i'm talking about ...

Sorry I don't recognize those measurements. Have you tried his forum?


http://www.instantboats.com/phpBB3/

Maybe the Yahoo group?

http://groups.yahoo.com/group/Instantboats/

let me guess...
the 2nd figure never greater or equal to 12 & 3rd digit never greater or equal to 8...
so
1.4.2 ->1ft 4 2/8 inches?
1.1.5 -> 1ft 1 5/8 inches?
0.11.1 -> 0ft 11 1/8inches?
0.11.7 -> 0ft 11 7/8inches?

That's what I thougt (all other part of the project are never greater or equal to 8)... but I'm totally ignorant on imperial system .... so I thought I was maybe missing something ....
thanks everybody
in any case I will ask the instant boat forum, thanks James

The forum is probably the fastest way to get an answer. My guess would be that maybe the first separator is a comma and the second separator is a period. Something like 1, 1.5 means one foot and 1.5 inches. I have never seen Imperial measurements like these.

Sergio,
The most accurate way to ensure the proper length is actually to the conversion in the native documents. The rounding or "alternate units" out of autocad when the dimensions were created can be set to round up or round down or be the most significant digit chosen. SInce the MM was created natively in the Metric (SI) units system, it's safer to use metric if you doing a lot of calcuations then convert at the end to reduce rounding errors.

During my build, I just used the metric measurements and converted. 25.4mm = 1 inch. I work in "imperial" units and this was the most accurate for my builds. example. So, if your cutting area is 48" x 96", that would be 1219.20mm x 2438.40mm

I have built three machines to date with great success keeping it all metric until that end of each equation.

Sean, I understand your point, but my problem/doubt is that I can't be sure of what is written on the project. 0,3,3 can be 3 inches 3/8 can be 3.3 inches, 3 inches 3/16 ... I thought it was just a question of my ignorance on using the imperial system but it it seems that this kind of notation it's just not clear. I can't be sure nor in mm nor in inch .... so maybe the x/8 is the right thing but to be sure before cutting .... I think I have to ask in the instant boat forum. Sorry, I thought that it was something clear for an imperial born people.
thanks

can you give me a drawing # that this occurs on? I may be able to clarify for you.

Sean, Sergio is not having problems with the MechMate drawings, he is trying to build a boat with it and the dimensional notation in the book he is working from does not make sense (not that any imperial dimensions make sense! :) ) Look at post 1 & 2 above.

oh...thanks Alan. That makes a bit more sense.

Ok, I had an answer !
for example: 0,8,2+ means: 0 feet,8 inches, 2/8 inch and + is 1/16 of inch .....
I'm very happy to live in a mm country !! :)
Ciao

You've found the right answer.

Boat offsets ("dimensions") are given as Feet, Inches, Eighths.

So 3-2-1 means 3'-2 1/8"

This isn't really an artifact of imperial dimensioning as it is a peculiarity of boatbuilding. Boatbuilders are the only ones who use this weird notation.

...Or theatrical lighting! A par 64 is 64 - 8ths in diameter (or 8 inches) I really should have picked up on the notation shorthand. Boatswains and Theater riggers came from the same place. Brad, your usually quick on this.....:)

Glad you got your resolution.

Sean

Standard dimensions for large boats are given in feet-inches-eights and sometimes a + or - (+ means add 1/16 or - means subtract 1/16).
For canoes and small boats, the dimensions can be feet-inches-sixteenths and the same + or - but this time 1/32. It depends on the designer and how accurate he wants to be. If the third value is larger than 7 ie 8 to 15, the last value will be in sixteenths eg 1 2 8- is 1 foot + 2 ins + 8/16 - 1/32 = 1 foot 2 15/32 ins.

The designer should give the information on which system is being used.

Metric is so much easier!!

Thanks to all !! Now everybody on the forum knows something more (starting from myself :-) ).

imperial vs metric

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